* {
    margin: 0;
    padding: 0;
    text-decoration: none;
}

#box {
    width: 750px;
    margin: auto;
}

nav {
    margin: auto;
    width: 750px;
}

nav ul {
    display: flex;
    justify-content: center;
}

nav ul li {
    list-style: none;
    margin-right: 50px;
}

#pic {
    width: 750px;
}

#pic img {
    display: none;
    position: absolute;
}

#pic img:nth-child(1) {
    display: block;
}